It is known to remove and replace a section of buried old pipe, such as a cast iron water main, using a "trenchless" procedure involving:
Digging pits at each end of the pipe section, to expose the pipe at those points; PA1 Breaking up and removing the exposed segments of old pipe, to thereby clear the pits; PA1 Installing a skid-mounted, rod string-tripping machine in the first pit, which machine is adapted to feed and withdraw a string of rods horizontally. The machine typically has one or more double-acting cylinders mounted in a frame for extension and contraction in a horizontal plane, together with means for releasably clamping onto the rod string, so that the cylinder rods and rod string may move longitudinally as a unit in the course of a cylinder stroke; PA1 Forming a string of rods (which have threaded pin and box couplings at their ends) having a radially expandable toothed dog assembly at its end and feeding it part way through the pipe section; PA1 Expanding the dog assembly to engage it with the old pipe; PA1 Actuating the rod string-tripping machine to advance the engaged portion of the old pipe section into the first pit in short lengths. Each such length of old pipe extending into the pit is then severed radially. The severed length of old pipe is removed. This process, of tripping the rod string with dog assembly in and out, to engage and remove sequential, discrete parts of the old pipe section, is continued until the entire pipe section has been removed; PA1 Threading the rod string back through the now pipe-free passageway, from the first pit to the second pit; PA1 Attaching an expander (that is, a cylindrical plug) to the second end of the rod string and pulling it back through the passageway, to increase its diameter; PA1 Removing the expander at the first pit and again threading the rod string back through the expanded passageway to the second pit; and PA1 Pulling the section of new pipe into the expanded passageway from the second pit using the rod string, to complete the replacement. PA1 first and second pits are dug at each end of a buried section of old pipe which is to be replaced; PA1 a cylinder-type rod string-tripping machine is emplaced in the first pit; and PA1 the machine is used to extend and withdraw a string of rods horizontally, as required, to accomplish the steps of pulling the old pipe into the first pit for break-up and removal, expanding the old passageway and pulling new pipe into the expanded passageway from the second pit. PA1 A string-tripping machine positioned in the first pit, with at least part of the exposed old pipe having been broken out beforehand so that the machine has access to the bore of the buried section of pipe, so as to extend its rod string thereinto; PA1 A string of rods extending from the string-tripping machine through the bore of the old pipe to a second pit where at least part of the old pipe exposed at that pit has also been broken out; PA1 Means for mechanically breaking up the old pipe as the latter is expelled. Said means are located in the pit into which the old pipe is being advanced. More preferably, the means comprises a stationary, hollow, conical member having its small end positioned adjacent the outlet from the old pipe passageway, so that old pipe being advanced will move over the small end of the conical member and the pipe will be split longitudinally and broken up as it continues to pass along the length of the conical member, said conical member forming a central passage therethrough for accommodating the rod string; PA1 A tool assembly attached to the second end of the rod string at the second pit. The tool assembly comprises a unit of sequentially connected components. More particularly, it comprises: means for centralizing the axis of the terminal end of the rod string in the bore of the old pipe; means for bearing against the annular second end face of the old pipe, so as to drive the old pipe ahead of it when pulled on; means for expanding the passageway which originally contained the old pipe; and means for engaging the new pipe to pull it into the expanded passageway behind the old pipe as the latter is expelled. More preferably, the centralizing means comprises a guide member adapted to fit snugly in the old pipe and the second means comprises a circular pull plate attached thereto. The guide member functions to centralize the pull plate so that it will bear evenly against the full extent of the annular second end face of the old pipe. Attached to the pull plate is the third means, for expanding the passageway as it passes therethrough. More preferably, the third means comprises a short cylinder or plug having an outside diameter that is slightly larger than that of the passageway through which the old pipe extends. The fourth means, for engaging the new pipe, may preferably comprise means for attaching to the front end of the new pipe or a rod and pull plate assembly that extends through the bore of the new pipe and bears against the annular surface of its rear end; and PA1 as a final integer, the string of new pipe to be emplaced in the expanded passageway. PA1 excavating first and second pits at the first and second ends of the section of old pipe to be removed and replaced, to thereby expose the pipe at those points; PA1 breaking up the two segments of exposed pipe, to clear the pits; PA1 inserting, in the first pit, first means for horizontally tripping a rod string; PA1 inserting, in the first pit, means for longitudinally splitting old pipe being advanced thereover, said second means being adapted to enable a rod string to extend therethrough; PA1 tripping a string of rods through the bore of the old pipe section; PA1 attaching, to the second end of the rod string, a tool assembly comprising, in sequence, second means for bearing against the annular second end face of the old pipe section, third means, secured to the second means, for expanding the diameter of the passageway as said third means passes therethrough, and fourth means, secured to the third means, for engaging new pipe to pull it into the expanded passageway, said fourth means having a section of new pipe associated therewith; and PA1 pulling on the first end of the rod string with the first means and progressively disassembling the rods as they become available in the first pit, thereby advancing the old pipe into the first pit and over the splitter means, whereby the pipe is split longitudinally, while simultaneously pulling the tool assembly through the old passageway to expand it and bring the new pipe into the expanded passageway until the section of old pipe has been replaced with new pipe.
Such a system is disclosed in U.S. Pat. No. 4,626,134, issued to Coumont.
The described system has some shortcomings. It involves repeated trips with the rod string through the old pipe bore and the passageway formed by the pipe in the soil. And it further involves fracturing the old pipe, that has been advanced into the first pit, along a vertical plane using a guillotine-type means, to yield a discrete short length of pipe, and then presumably manually breaking up and removing this length. This latter operation interrupts the continuity of the process and unites with the multiplicity of trips to stretch out the tim.RTM.needed to complete the replacement.
It is the objective of the present invention to provide an improved trenchless system whereby old pipe is replaced with new pipe in a single trip of the rod string.